Group III-V semiconductor devices are commonly used in high-speed, low-noise, and power applications. A Group III-V device refers to a semiconductor device formed using a compound having at least one Group III element and at least one Group V element. For example, gallium arsenide (GaAs) has been used in pseudomorphic high electron mobility transistors (pHEMTs). A Group III-V semiconductor device could be formed using one or multiple Group III-V compounds.
One specific “family” of Group III-V compounds includes gallium nitride (GaN) and other Group III-nitrides, referring to compounds having at least one Group III element and nitrogen. Group III-nitrides can be used in manufacturing high-speed and high-power discrete devices or integrated circuits. Gallium nitride is often desirable because it can withstand high operating temperatures and can provide high breakdown voltages compared to standard silicon devices. Gallium nitride can also typically provide good high-frequency performance and lower on resistances.
In various Group III-V devices (such as Group III-arsenide and Group III-phosphide devices), a two-dimensional electron gas (2DEG) layer forms at the interface of a barrier layer and a channel layer due to doping in the barrier layer. In other Group III-V devices (such as Group III-nitride devices), a two-dimensional electron gas layer can form as a result of polarization charges within crystallized materials. A two-dimensional electron gas layer typically represents a sheet of electrons where electrons are confined and can move freely within two dimensions but are limited in movement in a third dimension. In a conventional Group III-nitride device, for example, a two-dimensional electron gas layer may form at the interface of two different Group III-nitride layers.
Ideally, an electrical connection can be made through one or more of the layers to an electron gas layer. Conventional approaches for forming an electrical contact to an electron gas layer include etching one of the layers to form a recess for the electrical contact or doping one of the layers, such as by using a silicon or other implantation or through annealing and alloying of a deposited metal layer. However, each of these conventional approaches typically suffers from various drawbacks.